Prior to the explosive growth in the public's demand for data services, such as dial-up Internet access, the local loop access network transported mostly voice information. This present access network typically includes numerous twisted-pair wire connections between the plurality of user locations and a central office switch (or terminal). These connections can be multiplexed in order to more efficiently transport voice calls to and from the central office. The present access network for the local loop is designed primarily to carry these voice signals, i.e., it is a voice-centric network.
Today, data traffic carried across telephone networks is growing exponentially, and by many measures may have already surpassed traditional voice traffic, due in large measure to the explosive growth of dial-up data connections. The basic problem with transporting data traffic over this voice-centric network, and in particular the local loop access part of the network, is that it is optimized for voice traffic, not data. The voice-centric structure of the access network limits the ability to receive and transmit high-speed data signals along with traditional quality voice signals. Simply put, the access part of the network is not well matched to the type of information it is now primarily transporting. As users demand higher and higher data transmission capabilities, the inefficiencies of the present access network will cause user demand to shift to other mediums of transport for fulfillment, such as satellite transmission, cable distribution, wireless services, etc.
An alternative present local access network that is available in some areas is a digital loop carrier (“DLC”) system. DLC systems utilize fiber-optic distribution links and remote multiplexing devices to deliver voice and data signals to and from the local users. An early DLC system is described in U.S. Pat. No. 5,046,067 titled “Digital Transmission System” (“the '067 patent”). The '067 patent describes a Digital Loop Carrier (DLC) system. In a typical DLC system, a fiber optic cable is routed from the central office terminal (COT) to a host digital terminal (HDT) located within a particular neighborhood. Telephone lines from subscriber homes are then routed to circuitry within the HDT, where the telephone voice signals are converted into digital pulse-code modulated (PCM) signals, multiplexed together using a time-slot interchanger (TSI), converted into an equivalent optical signal, and then routed over the fiber optic cable to the central office. Likewise, telephony signals from the central office are multiplexed together, converted into an optical signal for transport over the fiber to the HDT, converted into corresponding electrical signals at the HDT, demultiplexed and routed to the appropriate subscriber telephone line twisted-pair connection.
Some DLC systems have been expanded to provide so-called Fiber-to-the-Curb (FTTC) systems. In these systems, the fiber optic cable is pushed deeper into the access network by routing fiber from the HDT to a plurality of Optical Network Units (ONUs) that are typically located within 500 feet of a subscriber's location. Multi-media voice, data, and even video from the central office location is transmitted to the HDT. From the HDT, these signals are transported over the fibers to the ONUs, where complex circuitry inside the ONUs demultiplexes the data streams and routes the voice, data and video information to the appropriate subscriber.